Specifications

As mentioned elsewhere, for the first season, the stock 5.3 HE engine and Turbo Hydro automatic transmission will be used to get through tech, and do the initial licensing runs which are in 25mph increments. With the addition of dual throttle intakes and headers, I hope to get past the 150mph mark on the salt with a little luck and limited slippage.

In the interests of thoroughness, here are the specs on the factory XJ-S configuration.

The Final engine will be an extensively modified, slightly stroked 6 liter V12.

The change over to a manual transmission is planned using a 4 speed Muncie close ratio transmission. The final drive ratio in this trans is 1:1. I do believe I will have to locate a 5 or 6 speed with finals in the overdrive range to get the most out of the combination. But, there is a budget on this project and it is limited.

I find the factory specs and drawings helpful not only when it comes to specific details, but also when visualizing solutions.

Looking at a blue print, it is easy to see why the flexable rubber front dam was added to stop lift. The bumper would act as a splitter causing all air below the bumper to go under the car causing a high pressure lift force. The rubber dam catches this air and redirects it to the side of the car lessening the problem. I say ‘lessening’, as the factory dam is made from flexible rubber, which is obviously not as rigid as 150mph performance would dictate it should be.

While obtaining advice from Group 44’s Chief Engineer Lankey Forshee, he was quick to point out that the cars were known to get light in the rear end around the 200mph mark. This too becomes very apparent when viewing the profile of the car. The sudden large open space behind the read window /passenger compartment creates a low pressure zone, resulting in a lift force on the rear of the car.

If you have seen a TWR (Tom Wilkenshaw Racing) car, you’ll be very aware of the spoiler that they used on the back boot/trunk lid of the car. One can assume this was at least part of the motivation for the spoiler. You’ll also notice in shots of the race TWR XJ-S, additional ‘special’ effects were added behind the rear wheels, below the bumper, to grab air and pull it in behind the car to reduce the drag of the trailing low pressure zone.

I haven’t mentioned the Group 44 body modifications as they are substantial and not allowed in the /PRO class this car will compete in, therefore of no importance to this project. Only ‘stock’ body design/panel placement can be used. I was fortunate to locate an original TWR ground effects package in the UK and imported it for use on this car as these panels were available to the general public and are therefore allowable. Although badly damaged, they are made of fiberglass and repairable. The initial work has been done to the panels so that they are once again complete and intact